The present invention relates to a photosensitive quinone diazide compound, and in particular to a positive working photosensitive composition as well as an electrodeposition composition containing this quinone diazide compound used for the preparation of a printed circuit board.
In the production of a printed circuit board wherein a positive working photoresist is used, it is known that a problem of relatively poor adhesion of the photosensitive resin to the base plate exists. This problem of poor adhesion can be improved by the adoption of an electrodeposition technique. In the electrodeposition technique, the electrodeposition coating used is a water soluble emulsion, and the components of the coating are suspended in the water in particulate form. As electrostatic repellent forces exist between these particulates, they will not precipitate during the electrodeposition operation. The electrodeposition coating can be divided into anionic electrodeposition coatings and cationic electrodeposition coatings according to the electrical properties of the emulsified particulates. In the anionic electrodeposition coating, the carboxy groups of the polymer neutralize the small molecular amines (which are neutralizing agents) to form a negatively charged polymer, while in the cationic electrodeposition coating, the amine groups of the polymer neutralize the small molecular acid (which is a neutralizing agent) to form a positively charged polymer. Upon the application of electricity, the charge carrying polymer and the small molecular neutralizing agent will move to anode and cathode so that the anionic polymer deposits on the anode due to loss of ionic properties by contacting hydrogen ions and the cationic polymer deposits on the cathode due to being reduced by hydroxy ions.
Conventionally used photosensitive compounds for positive working photoresists are quinone diazides. These photosensitive compounds can be grafted on the charge carrying polymers (one component system), or can be separated from the charge carrying polymers (multicomponent system) when the electrodeposition technique is used for the coating. Japan laid-open patent No. 63-297473 discloses a photosensitive composition containing quinone diazide group bearing maleic copolymers. Japan laid-open patents No. 64-4672, No. 64-90270 and U.S. Pat. No. 4,673,458 disclose photosensitive compositions containing quinone diazide bearing acrylic copolymers. And U.S. Pat. No. 4,681,923 discloses a quinone diazide group bearing modified phenolic novolak resin. All of the above mentioned photosensitive compositions belong to the one component electrodeposition coating system. As the groups of the above-mentioned photosensitive compositions are grafted on the charge carrying polymer, this results in a diminution of the flexibility of the compositions. Therefore, during the process of electrodeposition, pin holes form on the coating. Furthermore, the photosensitivity of the photosensitive groups is reduced after they are grafted on the polymer.
It is known that the photosensitivity of the photosensitive groups can be improved if the photosensitive groups are not grafted on the charge carrying polymers. For example, European Patent No. 0265387 discloses a photosensitive mixture which includes a photosensitive compound prepared by grafting quinone diazides on 2,4-dihydroxybenzophenone or 2,3,4-trihydroxybenzophenone, and a charge carrying acrylic resin or phenoic novolak resin. Although the photosensitivity of the photosensitive groups is improved, the photosensitive compounds have a poor solubility to the solvent used for the preparation of electro-deposition solution, and their compatability with the charge carrying polymers is also not satisfactory. Therefore, precipitation is formed in the electrodeposition solution during the electrodeposition process and pin holes are also formed on the resultant coating layer.